There's something in the primal act of moving swiftly through space under one's own power, without the encumbrance of machine or motivation, that just feels right, and doing so barefoot only serves to heighten that feeling. The health benefits of running are obvious, but it doesn't really take all that long to attain them. And then you start doing things like racing, or running long, long distances, or both, and at that point, the real question of why you're running is a fair one to ask. For me, running truly is an expression of who I am -- more comfortable alone than in groups, more inclined toward introspection than outward expression, more willing to spend long hours with only my thoughts and my will, not so much testing either, but simply examining their interplay. I want to run, and I CAN run, so I do. I don't have illusions that it will make me death-proof, or that I'll set any sort of record. It doesn't make me a better person, and it doesn't fix anything that's wrong with the world. It just feels as much a part of me as breathing. So, I run.
Okay, I just wanted to second this. Perfectly stated, it pretty much sums it up for me.